Throughout evolution, the human brain has developed ways of stopping us doing things that are likely to get us killed. This evolutionary trick served us very nicely throughout history; using intuition and a dose of experience, we build up an idea of what is safe in our world. For most of human history, what is unsafe, often led to death, which is widely agreed to be an unfavorable outcome.
This concept is commonly framed in the ideas of Comfort zone and Safety zone. Your comfort zone is the little zone within which you can go about your daily life without feeling you are going to take on any risk, like going down to your local hairdressers. This is the level to which your prehistoric mind is happy that you're unlikely to take on any real risk, you've got your hair done in the same way for a while and its therefore not something to get worked up about.
Your safety zone on the other hand is that feeling you start to get when you're stepping outside of that comfort zone. For example, visiting a new hairdresser. That voice in your head starts to tell you that perhaps this isn't such a good idea. You can think of many reasons how it might all go wrong and why you should have just stuck with the one you usually go to. What you often find though, is that you walk away from the experience realizing that there was not a real need to be that nervous in the first place, your hair looks nice (might even be nicer than usual) and perhaps unsurprisingly, you did not die. Your comfort zone has now adapted and more opportunities are now available to you because you are not scared of taking them.
There is of course an element of danger in our everyday lives (so don't close your eyes and cross the road) However, the honest truth is that most of the things we are scared of; public speaking, visiting a new hairdressers are unlikely to end in death. That interview you're nervous about might have some consequences if you mess it up, but its unlikely to have all the negative consequences you convince yourself it will.
Perhaps think about some of those things you've been putting off and ask yourself what opportunities might present themselves if you just went ahead and did it.
"Do one thing every day that scares you." – Eleanor Roosevelt.